Field of the Invention
The present invention relates to a valve reference position-learning device for an internal combustion engine, for learning a reference position of a valve which regulates flow of exhaust gases or intake air of the engine.
Description of the Related Art
Conventionally, as the learning device of this kind, one disclosed in the Publication of Japanese Patent No. 4434057 is known. This learning device learns a reference position of a wastegate valve that diverts exhaust gases from a turbine of a supercharger of an internal combustion engine. In this learning device, the learning of the reference position is performed after the warm-up of the engine. This takes into consideration that after the warm-up of the engine, when compared with before the warm-up, the temperature of the wastegate valve and a drive system therefor becomes higher and the reference position of the wastegate valve is displaced due to expansion (thermal elongation) of the drive system and the like caused by this temperature rise. Therefore, the learning of the reference position is performed only after the warm-up of the engine to avoid erroneous learning of the reference position.
In the conventional learning device, however, the learning of the reference position of the wastegate valve is performed on condition that the warm-up of the engine is completed, so that in a case where the engine is started in a cold state, it is impossible to learn the reference position until predetermined conditions are satisfied after completion of the warm-up. Therefore, before the reference position can be learned, if the reference position learned after the immediately preceding warm-up of the engine is used for control of supercharging pressure or the like, the reference position deviates from the position in the cold state in which there is no thermal elongation, which can degrade the control accuracy.
Further, it is also known that the reference position of the valve is learned at the time of start of the engine, e.g. by using a time period from the turn-on of an ignition switch to completion of the start (cranking) of the engine. In this case, however, when the turn-on operation of the ignition switch is immediately followed by a starting operation (quick start of the engine is performed), it is impossible to secure time required for learning, so that it is impossible to learn the reference position consistent with the cold state, which can cause the same problem as mentioned above.